Transcript Nerve activates contraction

Objective 8: TSWBAT
explain how cancerous cell
division is different from
normal cell division.
Cancer cells have escaped from cell cycle
controls
• Cancer cells divide excessively and invade other
tissues because they are free of the body’s control
mechanisms.
• Cancer cells do not stop dividing when growth factors are
depleted either because they manufacture their own, have
an abnormality in the signaling pathway, or have a
problem in the cell cycle control system.
• If and when cancer cells stop dividing, they do so at
random points, not at the normal checkpoints in the
cell cycle.
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• Cancer cell may divide indefinitely if they have a
continual supply of nutrients.
• In contrast, nearly all mammalian cells divide 20 to 50
times under culture conditions before they stop, age,
and die.
• Cancer cells may be “immortal”.
• Cells (HeLa) from a tumor removed from a woman
(Henrietta Lacks) in 1951 are still reproducing in
culture.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• The abnormal behavior of cancer cells begins
when a single cell in a tissue undergoes a
transformation that converts it from a normal cell
to a cancer cell.
• Normally, the immune system recognizes and destroys
transformed cells.
• However, cells that evade destruction proliferate to
form a tumor, a mass of abnormal cells.
• If the abnormal cells remain at the originating site,
the lump is called a benign tumor.
• Most do not cause serious problems and can be
removed by surgery.
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• In a malignant tumor, the cells leave the original
site to impair the functions of one or more organs.
• This typically fits the colloquial definition of cancer.
• In addition to chromosomal and metabolic
abnormalities, cancer cells often lose attachment to
nearby cells, are carried by the blood and lymph system
to other tissues, and start more tumors in a event called
metastasis.
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Fig. 12.17
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• Treatments for metastasizing cancers include highenergy radiation and chemotherapy with toxic
drugs.
• These treatments target actively dividing cells.
• Researchers are beginning to understand how a
normal cell is transformed into a cancer cell.
• The causes are diverse.
• However, cellular transformation always involves the
alteration of genes that influence the cell cycle control
system.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings